In a wireless communication system, such as one-way and two-way paging, that carries information, a receiver must perform certain tasks in order to recover the information. These tasks include timing recovery, frame synchronization and frequency offset correction. These tasks are typically implemented as three separate procedures that occur in sequence.
In prior art wireless communication systems using frequency shift keying (FSK) modulation, the receiver radio frequency (RF) front end typically has an analog discriminator output as the final output stage. This output is digitized and processed in a digital signal processor, microprocessor, or application-specific integrated circuit (ASIC). The amplitude of the discriminator output is proportional to the frequency deviation of the transmitted signal. The discriminator output must be mapped to bit values, or sliced, at the proper time as determined by the timing recovery. The bit values are used to determine correct frame synchronization. In addition, any frequency offset in the signal received causes the discriminator output to be shifted. This frequency offset must be removed prior to slicing.
If the tasks of timing recovery, frame synchronization and frequency offset correction are performed in sequence, either timing recovery or frequency offset correction is performed first and frame synchronization is completed last. If timing recovery is performed first, the timing recovery method must be tolerant of frequency offsets. Similarly, if frequency offset correction is performed first, the method used must be independent of symbol timing. In either case the time necessary to complete all of these three operations is due to each being performed sequentially with respect to the others. There is a desire to speed up the recovery of information in wireless systems. Therefore, what is needed is a way to speed up the timing recovery, frame synchronization and frequency offset correction in a wireless receiver.
The present invention provides for performing the three tasks of timing recovery, frame synchronization and frequency offset correction simultaneously.